The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPPthird generation partnership projectAPaccess pointBCCHbroadcast channelCAcarrier aggregationCCcomponent carrierCQIchannel quality informationDCAdynamical channel allocationDCHdynamical frequency hoppingDLdownlinkE-UTRANevolved universal terrestrial radio access networkFHfrequency hoppingHARQhybrid automatic repeat requestHeNBhome eNBIEEEinstitute of electronics and electrical engineersISMindustrial, scientific, medicalL1layer 1LTElong term evolution (E-UTRAN)LTE-Along term evolution advancedMACmedium access controlOFDMorthogonal frequency division multiplexingPCFICH physical control format indicator channelPCHpaging channelPDCCHphysical downlink control channelPHICHphysical HARQ indicator channelPRBphysical resource blockPUCCHphysical uplink control channelPCellprimary cellP-SCHprimary synchronization channelPHYphysicalRRCradio resource controlSCellsecondary cellSPSsemi-persistent schedulingSRSsounding reference signalSSsearch spaceS-SCHsecondary-synchronization channelSTAstationTDMtime-division multiplexingTVBDtelevision band deviceTVWStelevision white spaceUEuser equipmentULuplinkWLANwireless local area networkWiFiwireless fidelity (IEEE 802.11)
In the 3GPP LTE system there are to be heterogeneous networks made up of conventional macro eNBs operating in the same spectrum with home eNBs, micro eNBs and pico eNBs. FIG. 1A illustrates such a heterogeneous environment in which a UE 20 is operating at a location at which it can communicate with a macro eNB 22 and also with a home eNB 26. There may also be additional micro and/or pico cells in the same region. Whether or not the micro and pico eNBs are implemented as remote radio heads under control of the macro eNB, such a heterogeneous radio environment presents a challenging interference scenario. Mitigating this interference is now a work item in the 3GPP [see document RP-100383, entitled NEW WORK ITEM PROPOSAL: ENHANCED ICIC FOR NON-CA BASED DEPLOYMENTS OF HETEROGENEOUS NETWORKS FOR LTE; RAN#47; Vienna, Austria; 16-19 Mar. 2010]. Briefly, it shall consider techniques used in earlier releases (Release 8/9) and shall ensure backward compatibility for Release 8/9 terminals as well as minimize impact to the physical layer air interface.
There has also been research into ‘offloading’ traffic from licensed bands to unlicensed bands in such heterogeneous networks, to help prevent traffic bottlenecks in the conventional licensed bands. Unlicensed spectrum goes by several names such as license-exempt and shared bands, and by example include what is known as TV white spaces and the ISM bands (both 2.4 GHz under IEEE 802.11b and 802.11g; and 5 GHz under IEEE 802.11a). Interference may arise in the license-exempt bands due to devices operating in co-existing non-cellular systems, such as WiFi (IEEE 802.11), Zigbee (IEEE 802.15), Bluetooth, and USB wireless systems.
LTE cellular-traffic offloading to a license-exempt band is attractive for the increased bandwidth it offers, provided communications can be made reasonably reliable. To this end, the LTE eNB may be used to set up an LTE connection on the license-exempt band so as to retain control of the offloaded cellular-based traffic. But still there needs to be some solution to minimize interference between the LTE eNB and its device transmissions and any non-cellular devices in the license-exempt band, despite the fact that co-ordination with non-cellular systems on that license-exempt band may not be possible.
In the same vein, future deployments of LTE are to include carrier aggregation CA which might be utilized to help mitigate interference [see for example document RP-091440 entitled: CARRIER AGGREGATION FOR LTE, 3GPP RAN #46; Sanya, China; 1-4 Dec. 2009).
FIG. 1B illustrates the general CA concept for LTE/LTE-A. For a given UE there is assigned a PCell (alternatively termed a primary component carrier or PCC) which by example is backward-compatible with LTE Release 8/9 UEs (and therefore 20 MHz in bandwidth). That same UE may also have in its assigned set SCell#1, SCell#2 and SCell#3 (alternatively termed secondary component carriers SCCs), which for completeness SCell#3 is exemplarily shown as being non-contiguous in frequency with the other CCs, Any number of the SCells or none of them may be active for that UE at any given time, as coordinated with the macro eNB 22. Every UE 20 is to have its assigned PCell always active, and so the legacy UEs will be assigned one backward-compatible CC (e.g., its PCell) and no others. It is expected for 3GPP Release 11 (LTE-A) that there will be the capability for cross scheduling across Cells/CCs, and also that the different Cells/CCs may have different UL/DL configurations.
In some deployments, the macro eNB 22 of FIG. 1A may be operating on the PCell and one or more SCells while the HeNB 26 of FIG. 1A is operating on a different SCell as an interference mitigation scheme. Another scheme in IEEE 802.11af is to have the various devices contact a TVWS database to determine the primary systems (i.e. TV broadcasting) and then rely on Carrier Sensing Multiple Access/Collision Avoidance (CSMA/CA) mechanisms to avoid inter-WiFi system interference [see for example document IEEE 802.11-11-0089r0 entitled 11AF COEXISTENCE ASSURANCE DOCUMENT, by Cisco Systems and Research In Motion, 19 Jan. 2011].
While these may be effective in some cases, and in fact may be used in combination with the teachings below, what is needed in the art is a way to offload traffic onto license-exempt bands in a manner that enables the licensed network/eNB to maintain some control over the offloaded traffic and also to reasonably assure that the offloaded traffic will be reliably sent or received on the license-exempt band despite the network not having control over that band.